Meniere's Disease is one of the pathological entities characterized by endolymphatic hydrops of the cochlear and vestibular labyrinths. Hydrops can result from an alteration of ion transport properties of the epithelial cells bordering the endolymphatic system. Little is known about the cellular basis of the pathologic processes involved because data are lacking from normal as well as pathological systems concerning mechanisms of active secretion and absorption of ions and for ionic permeabilities. Endolymph Is unique in that it is the only extracellular fluid In the body with a high potassium concentration and low sodium concentration. This project will continue our study of the ion transport processes responsible for secretion of potassium and absorption of sodium in the vestibular labyrinth and cochlea by further utilizing our in vitro techniques. Specific parameters to be measured include transepithelial voltage and resistance, intracellular voltage and cell input resistance, luminal (apical) Ionic activities, cell volume (height) and currents through single ionic channels. The membrane characteristics will be deduced from the observed changes in the above parameters due to experimental changes in the composition of the solutions (including application of experimental and ototoxic drugs) in contact with the apical and basolateral cell membranes.